Exploration for Fractured Reservoirs in Precambrian Basement Rocks of Texas Panhandle: An Integrated Approach

Mark S. Manwaring, Bert A. Weimer

This paper describes a detailed integrated study of the buried basement rocks of the Gray County, Texas, area. The study area comprises parts of Gray, Carson, and Wheeler Counties in the Texas Panhandle. We mapped faults and basement structure by integrating aerial photographs and enhanced Landsat structural interpretations with various data, including magnetics, gravity, geomorphic, paleogeologic, well-log, fracture core, well-top, subsurface structural, and isopach mapping data. The present structural configuration of the basement is a complex system of faults, bounding horst, graben, and tilted fault blocks. Most deformation resulted from left-lateral, oblique-slip faulting during the Pennsylvanian through Early Permian. Fractures in several orientations have experienc d multiple episodes of opening and fluid circulation. The local relief of the basement results from a combination of structural deformation and paleoweathering. Basement production ranges from 1 to 700 BOPD. This variable rate primarily results from the fractured nature of the basement rocks. Depth to production averages 3,500 ft. Oil probably migrated from the Woodford Shale in the Anadarko basin into the basement along ubiquitous fractures, and accumulated in open fracture zones associated with faults. However, drilling within a fault zone does not assure basement production. Other geologic factors that are equally important to basement oil accumulations and production are fault orientation, fracture type, fracture mineralization, degree of weathering, basement subcrop elevation, litho ogy, fault intensity, proximity to fault-associated fracture zone, and treatment procedures.

The approach used in this study is significant. By integrating a variety of data types with more than 10 orders of magnitude of scale difference, we obtained a reliable picture of the geology, and defined the areas most likely to have oil accumulations.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.